The present invention relates to implants and methods for joint fusion. More specifically, the invention relates to implants, instrumentation and methods for fusing a sacroiliac joint.
The sacroiliac (SI) joints are formed by the connection of the sacrum and the right and left iliac bones. While most of the spinal vertebrae are mobile, the sacrum is made up of five vertebrae that are fused together and do not move. The iliac bones are the two large bones that make up the pelvis. As a result, the SI joints connect the spine to the pelvis, and form the largest axial joints in the body. The sacrum and the iliac bones are held together and supported by a complex collection of strong ligaments. There is relatively little motion at the SI joints; there are normally less than 4 degrees of rotation and 2 mm of translation at these joints. Most of the motion in the area of the pelvis occurs either at the hips or the lumbar spine. These joints support the entire weight of the upper body when it is erect, placing a large amount of stress across them. This can lead to wearing of the cartilage of the SI joints. Some causes of degeneration and/or pain in the SI joints include osteoarthritis, pregnancy, leg length discrepancy, gout, rheumatoid arthritis, psoriatic arthritis, reactive arthritis, and ankylosing spondylitis.
Treatment options have been limited to conservative care involving physical therapy and joint injections or traditional open SI joint arthrodesis surgery until recently. Open arthrodesis procedures reported in the literature require relatively large incisions, significant bone harvesting, and lengthy hospital stays; moreover, they may require non-weight bearing for several months.
The systems and methods for sacroiliac joint fusion disclosed here can be used to provide SI joint arthrodesis in a minimally invasive procedure. SI joint fusion using the systems and methods disclosed herein may provide advantages which can include a small incision, relatively short operating time with fewer steps, minimal blood loss, and a relatively short period of postoperative immobilization. For example, the steps disclosed herein for creating a cavity in the joint, filling it with graft material, and inserting a fusion device, may all be accomplished through a single access cannula in a single procedure. The size and configuration of the cutting instrument allows insertion into a bone or joint through a relatively narrow pathway, and creation of an undercut cavity within the bone or joint. Due to the shape and rigid construction of the blade disclosed herein and its assembly within the cutting instrument, the bone cutting instrument disclosed herein may create a cleaner cavity in a relatively short time, without the need to switch out blade members or employ multiple cutting instruments. Implants for joint fusion are disclosed herein, including an embodiment for SI joint fission having a design which is based on specific anatomical measurements of the ilium, sacrum, and SI joint space. An embodiment of the implant includes a fusion zone specifically sized to span the SI joint and provide compression for long-term joint fixation, and a threaded engagement zone specifically sized to extend to and anchor in the body of the sacral vertebra.